High resistivity soft magnetic material for miniaturized power converter

ABSTRACT

An on-chip magnetic structure structure includes a magnetic material comprising cobalt in a range from about 80 to about 90 atomic % (at. %) based on the total number of atoms of the magnetic material, tungsten in a range from about 4 to about 9 at. % based on the total number of atoms of the magnetic material, phosphorous in a range from about 7 to about 15 at. % based on the total number of atoms of the magnetic material, and palladium substantially dispersed throughout the magnetic material.

DOMESTIC PRIORITY

This application is a continuation of and claims priority from U.S.patent application Ser. No. 14/744,127, filed on Jun. 19, 2015, entitled“HIGH RESISTIVITY SOFT MAGNETIC MATERIAL FOR MINIATURIZED POWERCONVERTER”, which is a continuation of U.S. patent application Ser. No.14/666,624, filed on Mar. 24, 2015, entitled “HIGH RESISTIVITY SOFTMAGNETIC MATERIAL FOR MINIATURIZED POWER CONVERTER”, the entire contentsof both applications which are incorporated herein by reference.

BACKGROUND

The present invention relates to magnetic materials, and morespecifically, to magnetic materials for miniaturized power converters.

The technologies for power conversion devices are transitioning fromon-board collections of discrete components to compactly packagedcollections of power conversion components on increasingly smallerscales. However, the miniature compact packages may need to besupplemented with additional discrete inductive components.

On-chip inductive components include high energy density materials, suchas magnetic materials. Ferrite-based materials and metallic alloys areexamples of magnetic materials. Such materials can have thicknessesranging from hundreds of nanometers (nm) to a few microns. However,ferrite materials are generally processed at high temperatures (e.g.,higher than 800° C.), which are not compatible with complementarymetal-oxide semiconductor (CMOS) chip wiring processing temperatures.NiFe, CoFe, and CoZrTa are examples of magnetic alloys.

Magnetic metals can be deposited by vacuum deposition technologies(e.g., sputtering), electrodeposition, and electroless deposition inaqueous solutions. Vacuum deposition methods can be used to deposit alarge variety of magnetic materials. Electrodeposition is used for thedeposition of thick metal films because of its high deposition rate,conformal coverage, and low cost. Vacuum methods, however, can sufferfrom low deposition rates, poor conformal coverage, and the derivedmagnetic films are difficult to pattern.

Compared to ferrite materials, magnetic alloys can have higherpermeability and magnetic flux density, which are necessary to achievehigh energy density for on-chip devices. However, the resistivity ofmagnetic alloys can be low (e.g., less than 50 micro-ohm(μΩ)·centimeters(cm)). Further, because many on-chip devices are operated at highfrequencies (e.g., higher than 10 megahertz (MHz)), large eddy currentscan be induced within magnetic core. Eddy currents are circular electriccurrents induced within conductors by a changing magnetic field andresult high AC losses at high frequencies. One method to reduce eddycurrents is to increase the resistivity of the soft magnetic material sothat the eddy currents are confined within each individual magneticlayer. Also thinner magnetic layers have a larger effective magneticresistance, which results in smaller eddy currents.

SUMMARY

According to an embodiment of the present invention, an on-chip magneticstructure includes a magnetic material including cobalt in a range fromabout 80 to about 90 atomic % (at. %) based on the total number of atomsof the magnetic material, tungsten in a range from about 4 to about 9at. % based on the total number of atoms of the magnetic material,phosphorous in a range from about 7 to about 15 at. % based on the totalnumber of atoms of the magnetic material, and palladium substantiallydispersed throughout the magnetic material.

According to another embodiment, a method for forming an on-chipmagnetic structure includes activating a magnetic seed layer withpalladium, the magnetic seed layer being positioned over a semiconductorsubstrate; and electrolessly plating a magnetic alloy onto the palladiumto form a Pd/CoWP layer; wherein the Pd/CoWP layer includes cobalt in arange from about 80 to about 90 at. % based on the total number of atomsof the magnetic material, tungsten in a range from about 4 to about 9at. % based on the total number of atoms of the magnetic material,phosphorous in a range from about 7 to about 15 at. % based on the totalnumber of atoms of the magnetic material, and palladium substantiallydispersed throughout the magnetic material.

Yet, according to another embodiment, a method for forming an on-chipmagnetic structure includes activating a magnetic seed layer withpalladium, the magnetic seed layer being positioned over a semiconductorsubstrate; and electrolessly plating a magnetic alloy onto the palladiumin the presence of a magnetic field bias to form a film; wherein thefilm comprises cobalt in a range from about 80 to about 90 at. % basedon the total number of atoms of the magnetic material, tungsten in arange from about 4 to about 9 at. % based on the total number of atomsof the magnetic material, phosphorous in a range from about 7 to about15 at. % based on the total number of atoms of the magnetic material,and palladium substantially dispersed throughout the magnetic material.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a substrate having an adhesionlayer, a seed layer, and a protective layer;

FIG. 2 is a cross-sectional view of the substrate of FIG. 1 having alithographic resist mask patterned on the seed layer;

FIG. 3 is a cross-sectional view of the substrate of FIG. 2 having theprotective layer, the seed layer, and the adhesion layer patterned;

FIG. 4 is a cross-sectional view of the substrate of FIG. 3 having theresist layer and the protective layer removed;

FIG. 5 is a cross-sectional view of the substrate of FIG. 4 having theseed layer palladium activated;

FIG. 6 is a cross-sectional view of the substrate of FIG. 5 having anelectrolessly plated layer formed on the palladium activated layer;

FIG. 7A is a graph showing moment as a function of applied field for anas-deposited Pd/CoWP layer.

FIG. 7B is a graph showing moment as a function of applied field for aPd/CoWP layer after annealing to 200° C. for 1 hour.

DETAILED DESCRIPTION

Disclosed herein are electroless plating methods and materials formedfrom such methods. The methods and materials are used to form on-chipmagnetic structures, such as on-chip inductors or transformerstructures, e.g., closed-yokes or shielded-slab structures.

In one embodiment, an on-chip magnetic structure includes a magneticmaterial including cobalt in a range from about 80 to about 90 at. %based on the total number of atoms of the magnetic material, tungsten ina range from about 4 to about 9 at. % based on the total number of atomsof the magnetic material, phosphorous in a range from about 7 to about15 at. % based on the total number of atoms of the magnetic material,and palladium substantially dispersed throughout the magnetic material.The materials are referred to as Pd/CoWP materials or layers.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

As used herein, the articles “a” and “an” preceding an element orcomponent are intended to be nonrestrictive regarding the number ofinstances (i.e., occurrences) of the element or component. Therefore,“a” or “an” should be read to include one or at least one, and thesingular word form of the element or component also includes the pluralunless the number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” arenon-limiting terms and not intended to refer to any single aspect of theparticular invention but encompass all possible aspects as described inthe specification and the claims.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

As used herein, the terms “atomic percent,” “atomic %,” and “at. %” meanthe number of atoms of a pure substance divided by the total number ofatoms of a compound or composition, multiplied by 100.

It is to be understood that the on-chip magnetic structures will bedescribed in terms of a given illustrative architectures having a waferor semiconductor substrate. However, other architectures, structures,substrate materials, process features and steps may be varied.

It will also be understood that when an element, such as a layer,region, or substrate is referred to as being “on” or “over” anotherelement, it can be directly on the other element or intervening elementsmay also be present. In contrast, when an element is referred to asbeing “directly on” or “directly over” another element, there are nointervening elements present.

It will also be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

The design for an integrated circuit chip may be created in graphicalcomputer programming language and stored in a computer storage medium,such as a disk, tape, physical hard drive, or virtual hard drive (e.g.,a storage access network). If the designer does not fabricate the chips,or the photolithographic masks used to fabricate chips, the designer maytransmit the resulting design by physical means (e.g., by providing acopy of the storage medium storing the design) or electronically (e.g.,through the internet) to such entities, directly or indirectly. Thestored design is then converted into the appropriate format (e.g.,GDSII) for the fabrication of photolithographic masks, which can includemultiple copies of the chip design in question that are to be formed ona wafer. The photolithographic masks define areas of the wafer (and/orthe layers thereon) to be etched or otherwise processed.

Methods as described herein may be used to fabricate integrated circuitchips. The resulting integrated circuit chips can be distributed by thefabricator in raw wafer form (as a single wafer with multiple unpackagedchips), as a bare die, or in a packaged form. When packaged, the chip ismounted in a single chip package (e.g., a plastic carrier with leadsaffixed to a motherboard or other higher level carrier) or in amultichip package (e.g., a ceramic carrier that has either or bothsurface interconnections or buried interconnections). Following anyfabrication or packaging form, the chip is then integrated with otherchips, discrete circuit elements, and/or other signal processing devicesas part of an intermediate product, such as a motherboard, or an endproduct. The end product can be any product that includes integratedcircuit chips, ranging from toys and other low-end applications toadvanced computer products having a display, a keyboard or other inputdevice, and a central processor.

Reference in the specification to “one embodiment” or “an embodiment” ofthe present principles, as well as other variations thereof, means thata particular feature, structure, characteristic, and so forth describedin connection with the embodiment is included in at least one embodimentof the present principles. Thus, the appearances of the phrase “in oneembodiment” or “in an embodiment”, as well any other variations,appearing in various places throughout the specification are notnecessarily all referring to the same embodiment.

As used herein, the term “resistance” means the opposition to thepassage of an electric current through a conductor. Sheet resistancemeasurements herein are obtained with a Magnetron Instruments M7004-point probe immediately after deposition, as well as after annealing.An average resistivity is calculated from the sheet resistivityutilizing the total film thicknesses involved. The seed and platedlayers have different resistivities, and the layer resistivity may varywithin the individual layer thicknesses. However, the average value fora representative total thickness is characteristic of the resistivitywhat will be relevant in electrical usage.

As used herein, the term the “coercivity,” or “H_(c),” is a measure ofthe ability of a ferromagnetic material to withstand an externalmagnetic field without becoming demagnetized. Thus, the coercivity isthe intensity of the applied magnetic field necessary to reduce themagnetization of that material to zero after the magnetization has beendriven to saturation. Coercivity is reported in units of oersted (Oe) orampere/meter. Ferromagnetic materials with high coercivity are calledmagnetically “hard” materials. Materials with low coercivity aremagnetically “soft” materials. Coercivity is determined by measuring thematerial's magnetic hysteresis loop, also called the magnetizationcurve. Magnetic hysteresis loop measurements herein are performed usinga Vibrating Sample Magnetometer (VSM), MicroSense Model 10, on about 1inch square samples. The applied magnetic field is varied from −100 Oeto +100 Oe. The applied field where the data line crosses zero is thecoercivity.

As used herein, the term “magnetic anisotropy” means the directionaldependence of a material's magnetic properties. Depending on theorientation of the magnetic field with respect to the material'scrystalline lattice, a lower or higher magnetic field is necessary toreach the saturation magnetization. The “easy axis” is the directioninside a crystal, along which a small applied magnetic field issufficient to reach the saturation magnetization. The “hard axis” is thedirection inside a crystal, along which a large applied magnetic fieldis needed to reach the saturation magnetization.

Referring now to the drawings in which like numerals represent the sameor similar elements and initially to FIGS. 1-6, an electroless platingprocess for forming an on-chip magnetic component is illustrativelyshown. The magnetic components can be inductors, transformers, magneticyokes, magnets, and the like.

Referring to FIG. 1, an optional adhesion layer 120 is deposited onto asubstrate 110, which can be any semi-conductor substrate. The adhesionlayer 120 is used to improve the adhesion between a seed layer 130 andthe substrate 110. The adhesion layer 120 may include chromium,manganese, tungsten, molybdenum, ruthenium, palladium, platinum,iridium, rhenium, rhodium, osmium, titanium, tantalum, tungsten nitride,molybdenum nitride, titanium nitride, tantalum nitride, rutheniumnitride, iridium nitride, rhenium nitride, rhodium nitride, osmiumnitride, manganese nitride, or any combination thereof. Although, othermaterials may be employed in the adhesion layer 120. Seed layer 130 isdeposited either onto substrate 110 or the adhesion layer 120. Thesubstrate 110 may be part of a wafer or may be a stand-alone substrate.The substrate 110 may include silicon or other substrate material, e.g.,GaAs, InP, SiC, or any combination thereof.

The seed layer 130 may be formed using a physical-vapor-deposition (PVD)process (e.g., sputtering) or an electroless/electrolytic depositionprocess. A bias magnetic field can be applied during seed layer 130deposition to produce magnetic anisotropy. The seed layer 130 includes ametal, for example a metal or combination of metals with magneticproperties or a non-magnetic layer. The seed layer 120 can includenickel, cobalt, iron, manganese, boron, phosphorous, platinum,palladium, ruthenium, iridium, rhodium, rhenium, tungsten, molybdenum,titanium, tantalum, copper, gold, or any combination thereof. In oneembodiment, the seed layer 130 includes nickel in an amount in a rangefrom about 60 to about 95 at. % and iron in an amount in a range fromabout 5 to about 40 at. %. For example, the seed layer 130 can includeabout 80 wt. % nickel and about 20 wt% iron (Ni₈₀Fe₂₀). The seed layer130 can have a thickness of at least about 60 nm. Because the palladiumactivation (described below in FIG. 5) etches about 10-20 nm of the seedlayer 130, the seed layer 130 cannot be too thin. When the seed layer istoo thin, the electrolessly plated films deposited thereon are moresusceptible to degradation of coercive force even at low temperature.Thus, without being bound by theory, it is believed that adhesion andstrain of films deposited on very thin seed layers is inadequate tocreate a stable amorphous microstructure, resulting in degradation ofmagnetic properties at low temperatures. In one embodiment, the seedlayer 130 is from about 50 to about 70 nm thick. In another embodiment,the seed layer 130 is from about 45 to about 95 nm thick. Yet, inanother embodiment, the seed layer 130 is from about 10 to about 200 nmthick, or at least about 40 nm thick.

A top layer or protective layer 140, which is optional, may be employedto protect the seed layer 130. The top layer 140 may include, forexample, titanium, although any metal or non-metal may be employed. Thepassive top layer 140 may be removed just before electroless plating toensure a pristine seed layer 130 surface.

Referring to FIG. 2, a resist 210, such as a photoresist, is applied toa surface of the seed layer 130 or to the top layer 140, if employed.The resist 210 is patterned to achieve the desired shape of the seedlayer 130, as will be described.

Referring to FIG. 3, lithographic patterning of the seed layer 130 isperformed. Lithographic patterning includes transferring the pattern ofthe patterned resist 210 into the adhesion and top layers 120, 140, ifemployed. In any case, the seed layer 130 is patterned using the resist210. A wet etch may be employed to remove the seed layer 130, andoptionally the adhesion layer 120, from field region 310. The resist 210and the untreated top layer 140 may be removed to expose the pristineseed layer 130 in the appropriate shape onto which electrolesslydeposited structures may be formed. Other methods may also be employedto pattern or expose an appropriate seed layer 130 portion.

Referring to FIG. 4, the resist 210 (mask) is removed and the top layer140 is removed, if present. Palladium activation is performed on theseed layer 130. Palladium activation includes immersing the substrate110 in a palladium-containing solution. For example, a palladium sulfatesolution can be used. Other palladium-containing solutions and palladiumsalts and compounds can be used. Non-limiting examples of suitablepalladium salts include palladium chloride, palladium bromide, palladiumiodide, palladium acetate, palladium nitrate, or any combinationthereof. The amount of palladium in an activating solution is in anamount in a range from about 50 to about 60 parts per million (ppm). Inanother aspect, the amount of palladium in an activating solution isfrom about 10 to about 100 ppm. In an exemplary embodiment, palladiumsulfate is added to the seed layer in the presence of an acid. Examplesof suitable acids include sulfuric acid, hydrochloric acid, nitric acid,or any combination thereof. The emersion time and temperature forpalladium activation can generally vary.

Referring to FIG. 5, the palladium-containing solution dissolves aportion of the seed layer 130 and creates a thin layer of palladiumnanoparticles as an activated layer 510 on the seed layer 130 (activatedseed layer).

Referring to FIG. 6, an electrolessly plated layer 610 is formed on theactivated layer 510 of the seed layer 130. The electrolessly platedlayer 610 is a magnetic alloy including cobalt, tungsten, andphosphorous, and the resulting Pd/CoWP material 620 includes palladiumsubstantially dispersed throughout the electrolessly plated layer 610.Electrolessly plated layer 610 can be selectively electrolessly platedon the patterned seed layer 130 to form on-chip magnetic structures,such as yokes, coils, or other structures. The Pd/CoWP material 620 isamorphous or substantially amorphous. In another aspect, the Pd/CoWPmaterial 620 is a soft or substantially soft material and has an H_(c)of less than 1.0 Oe. In other embodiments, the Pd/CoWP material 620 hasan Hc of less than 5 Oe.

In another embodiment, the Pd/CoWP material 620 is free of granularstructures (e.g., grains), or is substantially free of granularstructures. Still yet, in other embodiments, the Pd/CoWP material 620 isfree of crystalline structures (e.g., crystals or nanocrystals), or issubstantially free of crystalline structures.

The substrate 110 is immersed in an electroless bath to formelectrolessly plated layer 610 and the resulting Pd/CoWP material 620.The Pd/CoWP material 620 can be a film. The Pd/CoWP material 620includes a cobalt in a range from about 80 to about 90 at. %, tungstenin a range from about 4 to about 9 at. %, and phosphorous in a rangefrom about 7 to about 15 at. %. In one aspect, cobalt is present in thePd/CoWP material 620 in an amount in a range from about 81 to about 86at. %. In another aspect, tungsten is present in the Pd/CoWP material620 in an amount in a range from about 4 to about 7 at. %. In anotheraspect, phosphorous is present in the Pd/CoWP material 620 in an amountin a range from about 9 to about 14 at. %, or from about 9 to about 11at. %. Cobalt can be present in an amount about or in any range fromabout 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, to 90 at. %. Tungsten canbe present in an amount about or in any range from about 4, 5, 6, 7, 8,to 9 at. %. Phosphorous can be present an amount about or in any rangefrom about 7, 8, 9, 10, 11, 12, 13, 14, to 15 at. %.

The thickness of the Pd/CoWP material 620 can generally vary. In oneaspect, the thickness of the Pd/CoWP material 620 in a range from about1 to about 2 microns. In another aspect, the thickness of the Pd/CoWPmaterial 620 is in a range from about 100 nm to about 2.5 microns. Yet,in another aspect, the thickness of the Pd/CoWP material 620 is in arange from about 200 nm to about 1.2 microns.

Electroless plating is performed in the presence of a field bias. Theapparatus can include a permanent magnet for applying a field bias,which can generally vary. In one embodiment, the field bias is fromabout 0.9 to about 1.1 Tesla during plating. The electroless solution isplaced between the magnetic poles. The electroless solution can beheated to a constant temperature. The substrate 110 to be electrolesslyplated is then placed inside the electroless solution. The surface ofthe substrate 110 is then coated with a seed layer 130, and optionallyan adhesive layer 120 and top layer 140. The seed layer 130 is depositedin the presence of an applied magnetic field to produce thin films withmagnetic anisotropy. The deposition time and temperature can generallyvary.

The above-disclosed ranges of cobalt, tungsten, and phosphorous on apalladium-activated seed layer provide a Pd/CoWP magnetic material withboth high resistivity and high magnetic flux. Generally, resistivity canbe compromised in materials having high magnetic flux. In CoWPmaterials, adding phosphorous can decrease magnetic flux. Althoughadding tungsten increases resistivity, merely combining cobalt,tungsten, and phosphorous alone does not provide the combination ofmagnetic flux and resistivity desired for miniaturized on-chip powerconverters. Thus, surprisingly, the method described herein forelectrolessly plating a layer of cobalt, tungsten, and phosphorous, inthe described proportions and on a palladium activated seed layer,provides a Pd/CoWP material with the desired properties. Slow depositionof the metals, as well as using palladium to activate the seed layer asdescribed provides a magnetic material in which palladium issubstantially dispersed throughout the CoWP electrolessly plated layer610. In contrast to other known methods and materials, palladiumgenerally functions as a seed layer remaining at the base of anelectrolessly plated magnetic material layer. Without being bound bytheory, it is believed that having palladium substantially dispersedthroughout the cobalt, tungsten, and phosphorous layer contributes tothe favorable properties of the magnetic material.

Following palladium activation, the palladium seed nucleation sites alsopin the microstructure of the Pd/CoWP and keep it amorphous to atemperature of at least 200° C. Grains or crystal formation within thePd/CoWP material results in films that are magnetically unstable. In oneembodiment, the Pd/CoWP described herein is substantially amorphous fromabout room temperature to 200° C. In another embodiment, the Pd/CoWP issubstantially amorphous from about 150 to about 240° C.

The electroless solution includes a source of cobalt, tungsten, andphosphorous, which can be any compound or salt thereof. The depositiontime and temperature can generally vary. In an exemplary embodiment, thedeposition rate is from about 1 to 10 nm per minute, and the depositiontime is from about 50 to about 200 minutes. In another exemplaryembodiment, the deposition temperature is from about 75 to about 120° C.

Non-limiting examples of suitable cobalt sources include cobalt salts,including cobalt sulfate, cobalt sulfate heptahydrate, cobalt nitrate,cobalt acetate, cobalt carbonate, cobalt citrate, cobaltacetylacetonate, cobalt carboxylates (e.g., cobalt acetate, cobaltformate, cobalt propanoate, cobalt butanoate, cobalt pentanoate, andcobalt hexanoate), or any combination thereof. The cobalt source may beincluded in a wide range of concentrations. In one embodiment, theconcentration is from about 50 millimolar (mM) to 100 mM. In anotherembodiment, the concentration is from about 60 mM to 80 mM.

Non-limiting examples of suitable tungsten sources include tungstatesalts. In one embodiment, tungsten salts include cationic groups ofalkaline or alkaline earth metals. Non-limiting examples of suitabletungstate salts include sodium tungstate, potassium tungstate, magnesiumtungstate, calcium tungstate, or any combination thereof. The tungstensource may be included in a wide range of concentrations. In oneembodiment, the concentration is from about 200 mM to 700 mM. In anotherembodiment, the concentration is from about 300 mM to 500 mM.

The electroless solution includes a source of phosphorous, which canalso function as a reducing agent. Non-limiting examples of a suitablephosphorous sources/reducing agents include sodium hypophosphite orsodium hypophosphite monohydrate. The sodium hypophosphite may beincluded in a wide range of concentrations. In one embodiment, theconcentration is from about 100 mM to about 500 mM. In anotherembodiment, the concentration is from about 250 mM to about 450 mM.

The electroless solution can include additives, such as one or more of abuffer, a complexing agent, a stabilizer, or a surfactant. Non-limitingexamples of suitable buffers include boric acid, carbonic acid,phosphoric acid, salts thereof, and mixtures thereof. Other examples ofsuitable buffers include piperidine salts and complexes, methylaminesalts and complexes, N-cyclohexyl-3-aminopropanesulfonic acid (CAPS)salts and complexes, 4-(cyclohexylamino)-1-butanesulfonic acid (CABS)salts and complexes, or any combination thereof. The concentration ofthe buffer is selected to achieve a desired pH of of about 8.0 to 10.0.

Non-limiting examples of suitable complexing agents include citric acid,lactic acid, tartaric acid, succinic acid, oxalic acids, amino acids,salts thereof, and mixtures thereof. The concentration of the complexingagent can generally vary. In one embodiment, the concentration of thecomplexing agent is from about 250 mM to 750 mM. In an exemplaryembodiment, the concentration of the complexing agent is from about 400to about 600 mM.

Suitable surfactants include non-ionic surfactants. Non-limitingexamples of suitable non-ionic surfactants include polysorbates,polyethylene glycol (PEG), 4-(1,1,3,3-tetramethylbutyl)phenol/poly(oxyethylene) polymers, poly(oxyethylene)-poly(oxypropylene)block copolymers, and the like, and mixtures thereof. In one embodiment,the surfactant is present in an amount from about 2.5 to about 7.5 ppm.In an exemplary embodiment, the surfactant is present in an amount fromabout 4 to about 6 ppm.

Non-limiting examples of suitable stabilizers include lead salts, suchas lead acetate and lead nitrate, cadmium salts, such as cadmium acetateand cadmium nitrate, or any combination thereof. In one embodiment, thestabilizer is present in an amount in a range from about 0.01 to about0.5 ppm. In an exemplary embodiment, the stabilizer is present in anamount from about 0.05 to about 10 ppm.

After electroless plating, annealing is performed in a vacuum furnace inthe presence of a magnetic field bias. The time and temperature forannealing can generally vary. In one embodiment, the electrolesslyplated substrates are annealed at a temperature from about 125 to 250°C. for a time from about 15 to 60 minutes. Additionally, electrolesslyplated substrates are further annealed to 200 to 250° C. in a forminggas or nitrogen atmosphere in order to induce stress relaxation andevaluate the effects on the magnetic properties in the post-annealedstate.

After a 200° C. anneal for 1 hour, Pd/CoWP films described hereinmaintain their magnetic properties, or are magnetically stable. Forexample, the difference in the hard axis H_(c) after deposition and thenafter annealing to 200° C. is less than about 0.5 Oe. In someembodiments, the difference in the hard axis H_(c) after deposition andannealing to 200° C. is less than 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, and0.1 Oe, indicating that the magnetic properties are maintained after theanneal. In another embodiment, the hard axis H_(c) is less 1.0 Oe. Yetin another embodiment, the Pd/CoWP is magnetically stable to at least200° C. for at least 1 hour.

The Pd/CoWP films also maintain high resistivity after annealing. In oneembodiment, the resistivity is at least 110 μΩ·cm after annealing. Inanother embodiment, the resistivity is at least 100 μΩ·cm afterannealing. Yet, in another embodiment, the resistivity is at least 105,at least 115, at least 120, or at last 125 μΩ·cm after annealing.

EXAMPLES Example 1

Silicon wafers were immersed in an electroless solution within adouble-jacketed glass beaker between the poles of a permanent magnet.Table 1 below shows the electroless bath composition. A field bias ofabout 1 Tesla was applied during electroless plating. A heater was usedto heat the water circulating in the external jacket of the beaker to aconstant temperature. The silicon wafers were oriented with the platedsurface being in line with the magnetic flux lines. The silicon waferswere coated with a nanometer thick vapor deposited seed layer ofNi₈₀Fe₂₀. The NiFe seed layer was deposited in the presence of anapplied magnetic field.

TABLE 1 Cobalt Sulfate Heptahydrate 0.07M Sodium Tungstate Dihydrate0.40M Sodium Hypophosphite Monohydrate 0.34M Citric Acid Anhydrous 0.50MBoric Acid 0.50M Lead Acetate 0.10 ppm Polyethylene Glycol 5.00 ppm pH 9Temperature 90° C. Palladium Sulfate - Bath Activation 55 ppm/10%H₂SO₄/3.0 min

Example 2

After electroplating in Example 1, the samples were annealed in a vacuumfurnace in the presence of a 1 Tesla magnetic field applied along theeasy axis. The annealing temperature was set to 200 or 250° C. for onehour. A temperature ramping rate of 5° C/minute was used, along with acooling rate of 5° C/minute under constant nitrogen flow.

Example 3

The magnetic properties of a sample with a 140 nm Pd/CoWP layer grown ona NiFe/Ti seed without an applied magnetic field were evaluated. Morethan half the initial thickness of NiFe seed was etched by the palladiumsolution. The palladium ions exchanged (deposited) with the iron thatreadily dissolved. As a result, the interface of the NiFe/Pd seed wassomewhat rough, which was reflected in the magnetic properties of the140 nm thin Pd/CoWP film that was deposited without a magnetic field.High values for the as-deposited coercive force (H_(c)) (9.0 Oe) andanisotropy field (H_(k)) (˜25 Oe) were observed. When the film wasannealed at 150° C. in the 1 Tesla field, the H_(c) of the hard axisimproved to 7.0 Oe. With further annealing to 250° C., magneticproperties did not degrade to be any worse than the properties of theas-plated film. Thus, it was concluded that the 140nm Pd/CoWP layer wasalso magnetically stable to 250° C.

Example 4

Films of thicknesses varying from 150 to 1,000 nm were evaluated. Thecompositions and thicknesses are shown in Table 2. Samples FX01-5, 6,D3, 7, 8, D4 were processed at a lower temperature (70° C. compared to90° C.) to assess the effect of deposition temperature. Sheet resistanceand resistivity were measured for the CoWP and the Pd/CoWP samples. Theresistivity of CoWP was measured to be about 73 to 95 μΩ·cm, and thecorresponding resistivity of the Pd/CoWP films was measured between 105and 149 μΩ·cm, which is within the desired resistivity range for anon-chip inductor.

TABLE 2 Plating Initial Final [Co] [W]at. % [P]at. % Pd NiFe Time AnnealT Res., Res., Sample at. % Thickness (Å) (Å) (Å) & T(° C.) pH (° C.)ohmcm ohmcm FX01-NiFe 600 21.2 seed FX01-1 83.5 ± 1 6.5 ± 1 10 ± 1 4600± 200 600 ± 50 100 min, 9.13 150 C. 30 min 74.5 73 90 C. 1 T/250 C. 1 hrFX01-2  85 ± 1  5 ± 1 10 ± 1 9000 ± 200 600 ± 50 200 min, 9.13 150 C. 30min 100 97.5 90 C. 1 T/250 C. 1 hr FX01-D1 84.5 ± 1 5.5 ± 1 10 ± 1 9700± 200 600 ± 50 230 min, 9.13 150 C. 30 min 96 95 90 C. 1 T/250 C. 1 hrFX01-3  85 ± 1  5 ± 1 10 ± 1 4600 ± 200 <10 400 ± 50 100 min, 9.13 150C. 30 min 110 105 90 C. 1 T/250 C. 1 hr FX01-4 84.5 ± 1 5.5 ± 1 10 ± 16900 ± 200 10 400 ± 50 200 min, 9.13 150 C. 30 min 124 122 90 C. 1 T/250C. 1 hr FX01-D2 83.5 ± 1 5.5 ± 1 11 ± 1 10000 ± 200  10 400 ± 50 230min, 9.13 150 C. 30 min 125 137 90 C. 1 T/250 C. 1 hr FX01-5  85.0 ± 0.5 5.0 ± 0.5 10.0 ± 0.5 1527 ± 100 430 ± 50 100 min, 9.13 150 C. 30 min 4038.25 70 C. 1 T/250 C. 1 hr FX01-6 85.5 ± 1 4.5 ± 1 10 ± 1 3600 ± 200400 ± 50 200 min, 9.13 150 C. 30 min 60 59.4 70 C. 1 T/250 C. 1 hrFX01-D3 85.5 ± 1 4.5 ± 1 10 ± 1 3000 ± 200 500 ± 50 230 min, 9.13 150 C.30 min 57.3 56.7 70 C. 1 T/250 C. 1 hr FX01-7  84.5 ± 0.5  5.2 ± 0.510.3 ± 0.5 1843 ± 100 25 ± 5 185 ± 50 100 min, 9.13 250 C. 15 min 127126.3 70 C. 1 Tesla FX01-8  84.2 ± 0.5  4.8 ± 0.5  11 ± 0.5 3011 ± 10014 ± 5 294 ± 50 200 min, 9.13 250 C. 15 min 116.1 115.2 70 C. 1 TeslaFX01-D4 85.0 ± 1 5.0 ± 1 10 ± 1 3500 ± 200 14 ± 5 200 ± 50 230 min, 9.13250 C. 15 min 156 149.4 70 C. 1 Tesla FX01-9 83.5 ± 1 5.5 ± 1 11 ± 17500 ± 200 14 ± 5 300 ± 50 200 min, 9.13 250 C. 15 min 122 120 90 C. 1Tesla FX01-10 83.0 ± 1 7.0 ± 1 10 ± 1 6600 ± 200 500 ± 50 200 min, 9.13250 C. 15 min 86 85.8 90 C. 1 Tesla FX01-D5 84.0 ± 1 6.0 ± 1 10 ± 1 8800± 200 14 ± 5 400 ± 50 230 min, 9.13 250 C. 15 min 114.4 113.8 90 C. 1Tesla

Example 5

The effects of anneals to 200° C. and lead acetate as a stabilizer wereevaluated. Table 3 shows the experimental parameters for depositing CoWPand Pd/CoWP films. Some samples were plated without lead acetate as astabilizer in the. Samples were annealed either at 200° C. or at 250° C.

The resistivity of the as-deposited CoWP layer was about 92 μΩ·cm,whereas an as-deposited Pd/CoWP had a resistivity of 118 μΩ·cm. Anothersample with Pd/CoWP had an as-deposited resistivity of 110 μΩ·cm. Theresistivity of the more than 1 μm thick Pd/CoWP films did not changewith annealing to 200° C. As determined by transmission electronmicroscopic (TEM) analysis, recrystallization of the amorphous materialwas found to be responsible for thermal instability (not shown). Thus,maintenance of the resistivity indicated that there no recrystallizationof the Pd/CoWP layers occurred.

FIG. 7A shows magnetics measurements of an 800 nm Pd/CoWP layer asdeposited in the presence of a 1 Tesla magnetic field (easy axis 710,hard axis 720). The hard axis H_(c) was 0.79 Oe; and

FIG. 7B shows the Pd/CoWP layer after annealing to 200° C. for 1 hour(easy axis 730, hard axis 740). The hard axis H_(c) was 0.65 Oe. Thus,the soft magnetic properties of the as-deposited Pd/CoWP layers eitherimprove or remain approximately constant with thermal annealing to 200°C. for 1 hour. Similar results (not shown) were obtained for 1.18 mmthick Pd/CoWP layers (H_(c)=0.77 Oe as deposited, and H_(c)=0.74 Oeafter 200° C. anneal for 1 hour).

However, when the chemistry of CoWP did not contain the lead acetate asa stabilizer, even annealing to 200° C. induced large grain growth (notshown). TEM analysis revealed that the grains grew to about 300 nm. Thevalue of the coercive force H_(c) of 1.7 Oe, also indicated that grainswere present.

Example 6

To further evaluate the effect of lead acetate on thermal stability andgrain growth, TEM was performed on plated CoWP and Pd/CoWP films thatwere stored for more than 1 month. The films that contained lead wereexceedingly more stable. The films were also amorphous. However, thefilms without lead exhibited substantial grain growth.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for forming an on-chip magneticstructure, the method comprising: activating a magnetic seed layer withpalladium to form a layer of palladium nanoparticles on a surface of themagnetic seed layer; and forming a magnetic alloy layer on the layer ofpalladium nanoparticles, the magnetic alloy layer comprising cobalt in arange from about 80 to about 90 at. % based on the total number of atomsof the magnetic alloy layer, tungsten in a range from about 4 to about 9at.% based on the total number of atoms of the magnetic alloy layer,phosphorous in a range from about 7 to about 15 at.% based on the totalnumber of atoms of the magnetic alloy layer, and palladium substantiallydispersed throughout the magnetic alloy layer.
 2. The method of claim 1,wherein the magnetic seed layer comprises nickel and iron.
 3. The methodof claim 1, wherein the on-chip magnetic structure is an inductor. 4.The method of claim 1, wherein the magnetic alloy layer is amorphous. 5.The method of claim 1, wherein the magnetic seed layer is at least 40 nmthick.
 6. The method of claim 1, wherein the magnetic alloy layer ismagnetically stable to at least 200° C. for at least 1 hour.
 7. Themethod of claim 1, wherein the cobalt is in a range from about 81 toabout 86 at %.
 8. The method of claim 1, wherein the magnetic seed layercomprises nickel and iron.